Cardiac magnetic field diagnosing apparatus by late ventricular potential and method of locating intramyocardial excitement uneven propagation portion

ABSTRACT

A magnetic field distribution measurement device ( 1 ) provides a non-contact magnetic measurement on a subject&#39;s chest at a plurality of coordinates and forms therefrom time-series magnetic field distribution data. A first arithmetic device ( 2 ) in response generates image data representing an intramyocardial excitation conduction rate. A second arithmetic device ( 3 ) receives a plurality of tomographic image data separately obtained by a tomographic diagnosis apparatus and processes the data to generate three-dimensional, anatomical image data. A display device ( 4 ) receives these data and displays on an anatomical image an image representing an intramyocardial excitation current. This can facilitate identifying an anatomical, positional relationship of a ventricular late potential caused in heart muscle. Furthermore, the anatomical image may be replaced with an image representing a normal stimulation conduction path and serving as a template.

TECHNICAL FIELD

[0001] The present invention relates generally to magnetocardiographicdiagnosis apparatuses for a ventricular late potential and methods ofidentifying a part in myocardium providing un-uniform conduction ofexcitation, and particularly to such apparatuses and methods employing anon-contact magnetic measurement to non-invasively diagnose athree-dimensional location of a ventricular late potential, or a part inmyocardium providing un-uniform conduction of excitation that mightcause ventricular tachycardia.

BACKGROUND ART

[0002] Conventionally, recording electrocardiograms has been generallyadopted as a technique to diagnose heart diseases.

[0003] However, conventional electrocardiography is insufficient forexample to determine the location, size and geometry of a part to betreated in a heart surgery and it cannot satisfactorily locate anaffected part.

[0004] This is attributed to the fact that electrocardiography is anindirect measurement methodology. Different subjects have differenttissues existing between their hearts and body surfaces, differentpositional relationships between their hearts and other organs andbones, their respective hearts having different sizes, a differentelectric conductance for each tissue of their bodies, and the like. Assuch, it has been significantly difficult to accurately determine anaffected part from information obtained from indirect measurement suchas electrocardiography.

[0005] A recent study has revealed that a macular texture that is formedin a normal myocardial tissue a period of time after the onset ofmyocardial infarction or attributed to cardiomyopathy or other similarheart diseases induces ventricular tachycardia.

[0006] Macular texture refers to a normal myocardial tissue with anecrosed or degenerated tissue existing therein in the form of anisland. In such a part of myocardium, un-uniform conduction ofexcitation is caused and a ventricular late potential is generated.Furthermore in such a macular texture a necrosed or degenerated tissueand a normal tissue have different electrical conduction characteristicsand accordingly a double excitation conduction path (a reentry circuit)can be formed.

[0007] More specifically, an excitation signal would circle in thisreentry circuit and as a result ventricular tachycardia is induced.Accordingly there exists a strong demand for three-dimensionally,accurately identifying such a part having a ventricular late potential.

[0008] Electrocardiography allows electrocardiography synchronizationaddition to be used to non-invasively detect whether a ventricular latepotential is present or absent. However, as has been described above, ithas been unable to three-dimensionally identify localization of a partin myocardium providing un-uniform conduction of excitation. An attempthas also been made to use multi-channel, electrocardiographicallymeasured data to determine the location, size and geometry of a parthaving a ventricular late potential. It is, however, insufficient inprecision to so determine the location and thus hardly satisfactory.

[0009] Currently, endocardial mapping using a catheter, which is a typeof invasive test, is employed to observe fragmented activity to identifya part in myocardium providing un-uniform conduction of excitation. Inparticular, a methodology has been adapted that uses a catheter toconduct an electrophysiological test to identify a part in myocardiumproviding un-uniform conduction of excitation and furthermore provide atreatment by catheter with a high frequency hypersthenia (catheterablation).

[0010] In this methodology, however, the catheter is inserted and movedwhile chest x-ray fluoroscopy is effected. Consequently, patients,doctors and radiographers are exposed to x-ray radiation over longperiods of time. In particular, doctors and radiographers suffer largeannual doses of x-ray radiation. Accordingly, there has been a strongdemand for significantly reducing the time required for conducting sucha test.

[0011] In a variety of fields a superconducting quantum interferencedevice (SQUID) magnetometer has been applied. It uses an SQUID capableof detecting with high sensitivity a magnetic flux of one billionth ofgeomagnetism. In particular, in the field of somatometry, which stronglydemands non-invasive measurement, as described above, an attempt isbeing made to use a SQUID magnetometer to provide a non-contact magneticmeasurement of human bodies.

[0012] In particular, the development of thin-film device fabricationtechnology in recent years has allowed the development of a DC-SQUID,and an attempt is being made to use a SQUID magnetometer to measure amagnetocardiogram, a distribution of a magnetic field of a heart.

[0013] However, a magnetocardiogram alone cannot directly display thelocation, size, and geometry of a part in myocardium providingun-uniform conduction of excitation, and it hardly allows doctors tocorrectly understand a relative, positional relationship of an affectedpart in a heart.

[0014] Accordingly it has been proposed to visualize an intramyocardial,electric current behavior from a magnetocardiographic distributionrepresented in a magnetocardiogram. One such approach adopted is to useone or more small current element pieces (current dipoles) to mimic thesource of a magnetic field for visualization. This methodology has beenconfirmed to be effective in determining the position of a bypasscircuit (a secondary conduction path) having-peculiarelectrophysiological characteristics in the WPW syndrome, e.g., a Kentbundle.

[0015] On the other hand, it has been confirmed that an excitationconduction path extending from a sinoauricular node to anatrioventricular node-a bundle of His-Purkinje fiber network can berepresented by a method using the above-described current dipole todetermine a source of a signal.

[0016] However, using one or more current dipoles to mimic a source of amagnetic field for visualization can only provide positional informationof the current dipole(s) corresponding to a specific time point and itcannot three-dimensionally identify the location, size and geometry of apart in myocardium that has a ventricular late potential, i.e., a partin myocardium providing un-uniform conduction of excitation.

[0017] The present invention therefore contemplates anmagnetocardiographic diagnosis apparatus for a ventricular latepotential and a method of identifying a part in myocardium providingun-uniform conduction of excitation that can employ a non-invasivemagnetic measurement to provide data representative of anintramyocardial, three-dimensional, electrical behavior and used tosafely, rapidly and with high precision, three-dimensionally identify apositional relationship of a part in myocardium that has a ventricularlate potential, i.e., a part in myocardium providing un-uniformconduction of excitation.

DISCLOSURE OF THE INVENTION

[0018] In accordance with the present invention a magnetocardiographicdiagnosis apparatus for ventricular late potential includes a magneticfield distribution measurement device, a first arithmetic device, asecond arithmetic device and a display device. The magnetic fielddistribution measurement device performs a non-contact magneticmeasurement on a subject's chest at a plurality of coordinates to obtaina plurality of time-series magnetic data corresponding to the pluralityof coordinates, and also using the plurality of time-series magneticdata to generate time-series magnetic field distribution data on thechest. The first arithmetic device uses the generated time-seriesmagnetic field distribution data to generate data representative of athree-dimensional, intramyocardial, electrical behavior of the subject.The second arithmetic device processes separately provided, tomographic,thoracic data of the subject to generate data representative of ananatomical image. The display device displays an image of thethree-dimensional, intramyocardial, electrical behavior represented bythe data generated by the first arithmetic device, as superimposed onthe anatomical image represented by the data generated by the secondarithmetic device, thereby capable of three-dimensionally identifyinglocalization of a ventricular late potential attributed tointramyocardial, un-uniform conduction of excitation.

[0019] Preferably the data generated by the first arithmetic device andrepresentative of the three-dimensional, intramyocardial, electricalbehavior is data representative of an intramyocardial excitationconduction rate.

[0020] More preferably the first arithmetic device approximates by meansof one or more small current element pieces a part in myocardiumcorresponding to an excitation conduction path and calculates a temporalvariation of a position of the small current element piece to generatedata representative of an intramyocardial excitation conduction rate.

[0021] Still more preferably the first arithmetic device operates basedon the calculated temporal variation of the position of the smallcurrent element piece to generate data representative of a difference inintramyocardial excitation conduction rate for each excitationconduction path.

[0022] In accordance with the present invention in another aspect amagnetocardiographic diagnosis apparatus for ventricular late potentialincludes a magnetic field distribution measurement device, an arithmeticdevice and a display device. The magnetic field distribution measurementdevice performs a non-contact magnetic measurement on a subject's chestat a plurality of coordinates to obtain a plurality of time-seriesmagnetic data corresponding to the plurality of coordinates, and alsousing the plurality of time-series magnetic data to generate time-seriesmagnetic field distribution data on the chest. The arithmetic deviceuses the generated time-series magnetic field distribution data togenerate data representative of a three-dimensional, intramyocardial,electrical behavior of the subject. The display device uses the datagenerated by the arithmetic device to superimpose together an imagerepresenting a stimulation conduction path of the subject extending froma sinoatrial node to a bundle of His-Purkinje fiber network and an imagerepresenting a three-dimensional, intramyocardial, electrical behaviorand display the images, thereby capable of three-dimensionallyidentifying localization of a ventricular late potential attributed tointramyocardial, un-uniform conduction of excitation.

[0023] Preferably the data generated by the arithmetic device andrepresentative of the three-dimensional, intramyocardial, electricalbehavior is data representative of an intramyocardial excitationconduction rate.

[0024] More preferably the arithmetic device approximates by means ofone or more small current element pieces a part in myocardiumcorresponding to an excitation conduction path and calculates a temporalvariation of a position of the small current element piece to generatedata representative of the intramyocardial excitation conduction rate.

[0025] Still more preferably the arithmetic device operates based on thecalculated temporal variation of the position of the small currentelement piece to generate data representative of a difference inintramyocardial excitation conduction rate for each excitationconduction path.

[0026] In accordance with the present invention in still another aspecta method of identifying a part in myocardium providing un-uniformconduction of excitation includes the steps of: performing a non-contactmagnetic measurement on a subject's chest at a plurality of coordinatesto obtain a plurality of time-series magnetic data corresponding to theplurality of coordinates and used to generate time-series magnetic fielddistribution data of the chest and generating first data representativeof a three-dimensional, intramyocardial, electrical behavior of thesubject from the generated time-series magnetic field distribution data;processing separately fed, tomographic, thoracic image data of thesubject to generate second data representative of an anatomical image;and displaying an image of the three-dimensional, intramyocardial,electrical behavior represented by the first data, as superimposed onthe anatomical image represented by the second data, to allowthree-dimensional identification of localization of a ventricular latepotential attributed to intramyocardial, un-uniform conduction ofexcitation.

[0027] Preferably the three-dimensional, intramyocardial, electricalbehavior represented by the first data is an intramyocardial excitationconduction rate.

[0028] More preferably the step of generating the first data uses one ormore small current element pieces to approximate a part in myocardiumcorresponding to an excitation conduction path and calculates a temporalvariation of a position of the small current element piece to generatedata representative of the intramyocardial excitation conduction rate.

[0029] Still more preferably the step of generating the first data usesthe calculated temporal variation of the position of the small currentelement piece to generate data representative of a difference inexcitation conduction rate for each excitation conduction path.

[0030] In accordance with the present invention in still another aspecta method of identifying a part in myocardium providing un-uniformconduction of excitation includes the steps of: performing a non-contactmagnetic measurement on a subject's chest at a plurality of coordinatesto obtain a plurality of time-series magnetic data corresponding to theplurality of coordinates and used to generate time-series magnetic fielddistribution data of the chest and generating data representative of athree-dimensional, intramyocardial, electrical behavior of the subjectfrom the generated time-series magnetic field distribution data; andusing the generated data to superimpose together an image representing astimulation conduction path of the subject extending from a sinoatrialnode to a bundle of His-Purkinje fiber network and an image representinga three-dimensional, intramyocardial, electrical behavior, and thusdisplaying the images to allow three-dimensional identification oflocalization of a ventricular late potential attributed tointramyocardial, un-uniform conduction of excitation.

[0031] Preferably the three-dimensional, intramyocardial, electricalbehavior represented by the data is an intramyocardial excitationconduction rate.

[0032] More preferably the step of generating the data uses one or moresmall current element pieces to approximate a part in myocardiumcorresponding to an excitation conduction path and calculates a temporalvariation of a position of the small current element piece to generatedata representative of the intramyocardial excitation conduction rate.

[0033] Still more preferably the step of generating the data uses thecalculated temporal variation of the position of the small currentelement piece to generate data representative of a difference in theintramyocardial excitation conduction rate of each excitation conductionpath.

[0034] Thus in accordance with the present invention an imagerepresenting a three-dimensional, intramyocardial, electrical behaviorobtained from a non-invasive magnetic measurement that is superimposedon anatomical image obtained by processing the same subject'stomographic, thoracic image data obtained by a separate, medicaldiagnosis apparatus can be displayed to allow doctors to safely, rapidlyand with high precision identify localization of a part having aventricular late potential, i.e., a part in myocardium providingun-uniform conduction of excitation that might cause ventriculartachycardia.

[0035] Furthermore in accordance with the present invention an imagerepresenting a three-dimensional, intramyocardial, electrical behaviorobtained from a non-invasive magnetic measurement that is superimposedon an image of a stimulation conduction path in the same subjectextending from a sinoauricular node to a bundle of His-a Purkinje fibernetwork can be displayed to allow doctors to safely, rapidly and withhigh precision identify localization of a part having a ventricular latepotential, i.e., a part in myocardium providing un-uniform conduction ofexcitation that might cause ventricular tachycardia.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In the drawings:

[0037]FIG. 1 is a functional block diagram schematically showing aconfiguration of a magnetocardiographic diagnosis apparatus forventricular late potential in accordance with the present invention in afirst embodiment;

[0038]FIG. 2 is a block diagram more specifically showing theconfiguration of the FIG. 1 apparatus;

[0039]FIG. 3 is a block diagram showing in detail a configuration of amagnetic field distribution measurement device shown in FIG. 2;

[0040]FIG. 4 shows by way of example an arrangement of a plurality ofmagnetic sensors on a front side of the chest of a subject;

[0041]FIG. 5 represents time-series magnetic data obtained from theplurality of sensors shown in FIG. 4, respectively;

[0042]FIG. 6 shows an example of a three-dimensional, anatomical imagedisplayed on a display device 4;

[0043]FIG. 7 is a flow chart for illustrating an operation of themagnetocardiographic diagnosis apparatus in accordance with the presentinvention in the first embodiment;

[0044]FIG. 8 is a functional block diagram schematically showing aconfiguration of a magnetocardiographic diagnosis apparatus forventricular late potential in accordance with the present invention in asecond embodiment;

[0045]FIG. 9 is a block diagram more specifically showing theconfiguration of the magnetocardiographic diagnosis apparatus inaccordance with the present invention in the second embodiment shown inFIG. 8;

[0046]FIGS. 10A and 10B schematically show a normal stimulationconduction path in a heart and an electrocardiographically representedwaveform;

[0047]FIG. 11 shows an image of a normal stimulation conduction path andan excitation conduction path, as displayed on a display device 6; and

[0048]FIGS. 12 and 13 are a flow chart for illustrating first and secondhalves, respectively, of an operation of the magnetocardiographicdiagnosis apparatus in accordance with the present invention in thesecond embodiment.

BEST MODES FOR CARRYING OUT THE INVENTION

[0049] Hereinafter, the present invention in embodiments willspecifically be described with reference to the drawings. Note that inthe figures, like components are denoted by like reference charactersand their descriptions will not be repeated.

First Embodiment

[0050]FIG. 1 is a functional block diagram schematically showing aconfiguration of a magnetocardiographic diagnosis apparatus forventricular late potential in accordance with the present invention in afirst embodiment.

[0051] As shown in FIG. 1, a magnetic field distribution measurementdevice 1 for example uses a measurement means such as a SQUIDmagnetometer, as will be described hereinafter more specifically, toprovide a non-contact magnetic measurement on a subject's chest at aplurality of coordinates to obtain a plurality-of time-series magneticdata corresponding to the plurality of coordinates. The plurality oftime-series magnetic data are then used to generate and outputtime-series magnetic field distribution data of a magnetic fieldexisting on the subject's chest, i.e., of the subject's heart.

[0052] The cardiac, time-series magnetic field distribution dataprovided by magnetic field distribution measurement device 1 is used bya first arithmetic device 2 for example employing a known calculationtechnique, as described hereinafter, to generate and output first datarepresenting a three-dimensional, intra-myocardial electrical behavior.

[0053] More specifically, the first arithmetic device 2 generates datarepresenting an intramyocardial excitation conduction rate. This rate isobtained, as will be described hereinafter, by using one or more smallcurrent element pieces, or current dipoles, to approximate a part inmyocardium that corresponds to an excitation conduction path, andcalculating the dipole/dipoles positional variation with time. From thecalculated variation, data of an excitation conduction rate can beobtained for each excitation conduction path. Consequently, localizationof a ventricular late potential attributed to un-uniform conduction ofexcitation can be determined.

[0054] Furthermore, magnetic resonance imaging (MRI), x-ray, computedtomography (CT), echocardiography, myocardial, single photon emissioncomputed tomography (SPECT) or any other similar tomographic diagnosisapparatus is used to separately obtain tomographic, thoracic image data(including data of a plurality of tomographic images) of the samesubject. The data are fed to a second arithmetic device 3 and processedthereby to generate and output second data representing athree-dimensional, anatomical image.

[0055] If the first data is represented in an image, and an electricalbehavior obtained in the first arithmetic device 2 corresponds to anintramyocardial excitation conduction rate, then by noting un-uniformityof an intramyocardial excitation conduction rate for each excitationconduction path displayed on a screen in some form, a part having aventricular late potential can be three-dimensionally identified.

[0056] Display device 4 superimposes an image representing athree-dimensional, intramyocardial electrical behavior (e.g., anexcitation conduction rate of each excitation conduction path)represented by the first data generated by the first arithmetic device,on a three-dimensional, anatomical image of a subject's chest that isrepresented by the second data generated by the second arithmetic device3, and displays the same. As a result, on an anatomical image,localization of a ventricular late potential in myocardium can beidentified three-dimensionally.

[0057]FIG. 2 is a block diagram more specifically showing theconfiguration of the magnetocardiographic diagnosis apparatus for aventricular late potential of the first embodiment shown in FIG. 1.

[0058] As shown in FIG. 2, magnetic field distribution measurementdevice 1 includes in a magnetic shield room (MSR) 11 a Dewar structure13 incorporating a SQUID magnetometer and arranged on the chest of asubject 12 to provide a non-contact magnetic measurement, and a magneticfield distribution data operation unit 14.

[0059] In Dewar structure 13 is provided a low-temperature environmentfilled with liquid helium to provide superconductance, and in theenvironment is accommodated a SQUID magnetometer configured of adetector coil formed of superconductor.

[0060]FIG. 3 is a block diagram more specifically showing a SQUIDmagnetometer 15 arranged in an ultra low temperature system provided inDewar structure 13 arranged in MSR 11 shown in FIG. 2, and operationunit 14 arranged in MSR 11 of a normal temperature system.

[0061] Note that the configuration shown in FIG. 3 is that for a singlechannel for measuring magnetic data of a single point on a subject'schest. As will be described hereinafter, in the present invention, on asubject's chest at a plurality of coordinates a magnetic field ismeasured, i.e., a multi-point, simultaneous magnetic measurement isprovided. Accordingly, MSR 11 of FIG. 2 would have therein the 1-channelconfiguration of FIG. 3 for each of channels required for a measurement.

[0062] With reference to FIG. 3, for a single channel a SQUIDmagnetometer generates magnetic data, as described hereinafter.

[0063] SQUID magnetometer 15 includes a pickup coil 16 formed ofsuperconductor for detecting a magnetic field generated from a surfaceof the chest of a subject. When pickup coil 16 captures a magneticfield, a current flows and drawn in by a coil 17 to create a magneticfield in an Nb shield 20.

[0064] Consequently, a magnetic field varying linearly relative to thatcreated in Nb shield 20 is formed in a superconducting loop 18. Voltagesof opposite ends of superconducting loop 18 are detected by an amplifierof operation unit 14 provided in MSR 11 of the normal temperaturesystem. Operation unit 14 adjusts a current flowing through a modulationcoil 19 provided in Nb shield 20 so that a detected voltage can thus befree of variation.

[0065] More specifically, the detection of an electric field of a humanbody by a SQUID is not a direct measurement of a magnetic fieldgenerated. Rather, a so-called a zeropotential method is used to providea feedback to allow a magnetic field in superconducting loop 18 to havea constant value (more specifically, a current flowing throughmodulation coil 19 is adjusted to control a magnetic field generated inmodulation coil 19 so that superconducting loop 18 internally,constantly has a constant magnetic field) to allow operation unit 14 toconvert to an electrical signal a magnetic field detected at pickup coil16 and output the signal. Such a feedback technique is typically a wellknown technique referred to as a flux locked loop (FLL).

[0066] Such a SQUID magnetometer 15 and its operation unit 14 are wellknown and will not further be described.

[0067] As has been described previously, the configuration shown in FIG.3 is that necessary for measuring magnetic data for a single channel andoutputs an electrical signal corresponding to time-series magnetic dataof a magnetic field measured on a front side of the chest of a subjectat a single point.

[0068] In the present invention, as has been described previously, alarge number of sensors (SQUID magnetometers) are arranged on a frontside of the chest of a subject to measure a magnetic field on the frontside at multiple points. A magnetic field varies with time and forexample even during a period corresponding to a single heart beat amagnetic field that is measured at different sites exhibits differentvariations depending on the sites.

[0069]FIG. 4 exemplarily shows an arrangement of a plurality of sensors(each corresponding to a SQUID magnetometer of a single channel) on afront side of the chest of a subject. Furthermore, FIG. 5 represents agroup of time-series magnetic data representing a variation of amagnetic field for the period of a single heart beat that is obtainedfrom the respective sensors of FIG. 4, as corresponding to theirrespective positions.

[0070] Magnetic field distribution measurement device 1 shown in FIG. 2outputs a group of time-series magnetic data corresponding to aplurality of positions (coordinates) for measurement, as shown in FIG.5. If a group of time-series magnetic data is captured with a particulartime noted, it is difficult to graphically (diagrammatically) representridges and troughs representing a distribution in intensity of amagnetic field present at a specific time on a front side of a chest tobe measured, and magnetic field distribution data represented in acontour map such as an atmospheric pressure represented in a weatherchart is accordingly obtained. In this sense also, data output frommagnetic field distribution measurement device 1 can be captured astime-series data of a distribution of a magnetic field on a front sideof a chest.

[0071] A group of time-series, magnetic data such as output frommagnetic field distribution measurement device 1, i.e., time-seriesmagnetic field distribution data are fed to the first arithmetic device2 of FIG. 2. The first arithmetic device 2 functions to obtain frommagnetic field distribution data an electrical behavior in the chest,e.g., an intramyocardial excitation conduction rate.

[0072] From the time-series magnetic field distribution data generatedby, magnetic field distribution measurement device 1 the firstarithmetic device 2 obtains three-dimensional information of anelectrical behavior in a human body at a part to be measured (a heart inthe present invention), e.g., an intramyocardial excitation conductionrate, as described hereinafter.

[0073] The first arithmetic device 2 approximates time-series, magneticfield distribution data generated by magnetic field distributionmeasurement device 1. In doing so, one or more small current elementpieces (i.e., current dipoles) are used. More specifically, the smallcurrent element pieces are scattered in a measured magnetocardiographicdistribution and a well known analysis methodology is employed todetermine a parameter (positional information and electric-currentvector) of each small current element piece with respect to a respectivepoint for measurement. Such an analysis methodology using currentdipoles is a well known technique, for example as specifically disclosedin Japanese Patent Laying-Open No. 5-157735, and it will not bedescribed herein in detail.

[0074] If the above analysis methodology is used to determine aparameter (i.e., position and electric current's direction) of eachsmall current element piece in a magnetocardiographic distribution thatcorresponds to a specific time point, then by observing the parameter'schronological variation, information regarding a current's conductionrate can be obtained.

[0075] The first arithmetic device 2 initially generates datarepresenting such a chronological variation of the position and electriccurrent's direction of a small current element piece, as describedabove, and feeds the data to display device 4 at one input. The firstarithmetic device 2 also uses the chronological variation to calculatean intramyocardial excitation conduction rate and the result may begenerated in the form of numerical data and furthermore may be generatedin the form of image data visibly representing the rate by an arrowhaving a length.

[0076] Thus the first arithmetic device 2 generates from the magneticfield distribution data generated by magnetic field distributionmeasurement device 1 a variety of forms of time-series data representingan intramyocardial excitation conduction rate to be analyzed, and inputthe generated time series data to display device 4 at one input.

[0077] The second arithmetic device 3 shown in FIG. 2 receives imagedata of a plurality of sliced images (for example a dozen of such imagesobtained at a pitch of five millimeters) of the chest of the samesubject that are previously taken using another tomographic analysisapparatus (not shown) such as MRI, x-ray CT, echocardiography ormyocardial SPECT with an electrocardiography synchronization triggerapplied.

[0078] The second arithmetic device 3 processes (interpolates) the dataof the plurality of sliced images and subjects the data tothree-dimensional, perspective conversion from a predetermined point ofview to generate second data representing an anatomical image. Thusforming a three-dimensional, anatomical image from a plurality of slicedimages is a well-known technique, for example as specifically disclosedin Japanese Patent Laying-Open No. 11-128224 and InternationalPublication WO 98/15226, and will not be described specifically.

[0079] Thus the second arithmetic device 3 generates the second datarepresenting a three-dimensional, anatomical image of the chest of thesame subject in a vicinity of his/her heart and feeds the second data todisplay device 4 at the other input.

[0080] Display device 4 of FIG. 2 superimposes on a three-dimensional,anatomical image of a subject's chest based on the second data from thesecond arithmetic device 3 an image based on the first data from thefirst arithmetic-device 2 and representing a chronological variation ofa position and a direction of a current of a small current element piecein myocardium.

[0081]FIG. 6 shows a manner of displaying a position and direction of asmall current element piece representing an intramyocardial excitationcurrent in a magnetocardiographic distribution at a specific time point,and an excitation conduction path before that time point is arrived at,as superimposed on a three-dimensional, anatomical image displayed bydisplay device 4.

[0082]FIG. 6 is a three-dimensional image obtained by interpolatingapproximately five tomographic images obtained by slicing a subject'schest at a pitch of five millimeters, for example. A depth of adisplayed image is difficult to represent by drawing. It is, however,intended to show a stereoscopic, anatomical image providing a sense of adepth that is formed by combining a plurality of sliced images.

[0083] In FIG. 6 an arrow A indicates the position and direction of asmall current element piece representing an intramyocardial excitationcurrent corresponding to the time point and its length represents themagnitude of the current. Furthermore, thick lines B, C, D represent atracing of an intramyocardial excitation conduction path obtained byapproximating a magnetic field of a heart by means of a small currentelement piece and more specifically, correspond to the small currentelement piece's positional variation chronologically linked together.

[0084] As such, for a part in myocardium with a low excitationconduction rate a small current element piece has its position varyingwith time to form a dense tracing, and for a part in myocardium with ahigh excitation conduction rate a small current element piece has itsposition varying with time to form a sparse tracing. As such, thesparseness/denseness of the position of a small current element piececonfiguring each of thick lines B, C, D representing an excitationconduction path displayed on a screen, allows their respective,intramyocardial excitation conduction rates to be visually recognized.

[0085] Furthermore, as has been described above, the first arithmeticdevice 2 may calculate the exact, each intramyocardial excitationconduction rate and display device 4 may display it numerically.

[0086] Thus on a perspective, three-dimensional, anatomical image anintramyocardial excitation conduction rate can be displayed for eachexcitation conduction path to allow doctors to correctly understand arelative, positional relationship of a part in myocardium having aventricular late potential, i.e., a part in myocardium providingun-uniform conduction of excitation on the anatomical image.

[0087]FIG. 7 is a flow chart of a method effected by themagnetocardiographic diagnosis apparatus of the first embodiment toidentify a part in myocardium providing un-uniform conduction ofexcitation.

[0088] In FIG. 7 initially at step S1 magnetic field distributionmeasurement device 1 is used to provide non-contact magnetic measurementon the chest of a human body at a plurality of coordinates, generate aplurality of time series data, and record the data if necessary.

[0089] Then at step S2 a plurality of MRI images taken with anelectrocardiography synchronization trigger applied are interpolated bythe second arithmetic device 3 (i.e., subjected to three-dimensional,perspective conversion from a predetermined point of view) to obtain athree-dimensional, anatomical image.

[0090] Then at step S3 an analysis start time point, an analysis endtime point and an analysis time interval are set to be t_(s), t_(e) andΔt, respectively.

[0091] Then at step S4 analysis start time point t_(s) is substitutedinto an analysis time point t to start an analysis. Then at step S5until analysis time point t reaches analysis end time point t_(e) thefollowing process is effected.

[0092] More specifically at step S6 the first arithmetic device 2approximates magnetocardiographic distribution data corresponding to adesignated analysis time point t, with one or a plurality of smallcurrent element pieces, to obtain data of the location, direction andmagnitude of an excitation current in myocardium.

[0093] Then at step Is the data of the location, direction and magnitudeof the intramyocardial excitation current at time point t−Δt, asobtained at step S6 of the previous loop preceding by time Δt, iscompared to the data corresponding to time point t, as obtained at stepS6 of the current loop, and an intramyocardial excitation conductionrate is calculated.

[0094] Then at step S8 display device 4 displays data representing anintramyocardial excitation conduction rate, as superimposed on ananatomical image having undergone a three-dimensional, perspectiveconversion from a predetermined point of view.

[0095] Then at step S9 Δt is added to analysis time point t.

[0096] Steps S6-S9 are repeated until a decision is made at step S5 thatanalysis time point t has reached analysis end time point t_(e). When itreaches analysis end time point t_(e) display device 4 terminatesdisplaying data representing the intramyocardial excitation conductionrate superimposed on the anatomical image.

[0097] Thus in the first embodiment an image representing anintramyocardial excitation conduction rate obtained from a SQUIDmagnetometer obtaining a non-invasive magnetic measurement on asubject's chest can be superimposed on a three-dimensional, anatomicalimage and thus displayed to allow a doctor to three-dimensionallyidentify the anatomical, positional relationship, size and geometry of apart in myocardium having a ventricular late potential, i.e., a part inmyocardium providing un-uniform conduction of excitation that mightcause ventricular tachycardia.

[0098] In particular, if high frequency catheter cauterization is usedto provide a treatment, it can previously, significantly narrow down aregion to be electrophysiologically tested using a catheter and a testconducted while radioscopy is provided can be conducted in asignificantly reduced period of time. Consequently, doctors andradiographers can avoid significantly large annual doses of x-rayexposure.

[0099] Furthermore, using the method of identifying a part in myocardiumproviding un-uniform conduction of excitation, as described in the firstembodiment, together with high frequency catheter cauterization allows aless invasive medical operation to be used to treat ventriculartachycardia and thus further alleviate a burden on patients.

Second Embodiment

[0100] In the first embodiment, forming an anatomical image entailsobtaining a large number of tomographic images of a subject and a testemploying MRI, x-ray CT or the like is accordingly, previouslyconducted. This results in an increased number of tests and an increasedburden on patients and also an obstacle to a treatment directly linkedto a test.

[0101] The present invention in a second embodiment can provide amagnetocardiographic diagnosis apparatus for ventricular late potentialand a method of identifying a part in myocardium providing un-uniformconduction of excitation that are capable of eliminating the formationof an anatomical image to conduct a reduced number of tests and carryout a diagnosis and a test such that they are directly linked.

[0102]FIG. 8 is a functional block diagram schematically showing aconfiguration of the magnetocardiographic diagnosis apparatus forventricular late potential in the second embodiment.

[0103] With reference to FIG. 8, magnetic field distribution measurementdevice 1 will not be described as it has been described in the firstembodiment.

[0104] Magnetic field distribution measurement device 1 generatestime-series, magnetic field distribution data and outputs the data to anarithmetic device 5 which in turn uses the received time-series,magnetic field distribution data and employs the aforementioned analysistechnique using a current dipole to generate data regarding anintramyocardial, three-dimensional electrical behavior, e.g., anintramyocardial excitation current. Arithmetic device 5 then uses thegenerated data of the excitation current to superimpose datarepresenting a ventricular, intramyocardial excitation (stimulation)conduction path of a period corresponding to that from anelectrocardiographically represented P wave to anelectrocardiographically represented QRS complex and data representingan intramyocardial excitation conduction rate on each other and outputsthe same to display device 6.

[0105] Display device 6 superimposes an image representing theintramyocardial excitation conduction rate represented by the datagenerated by arithmetic device 5, on a three-dimensional image of theexcitation conduction path also obtained by arithmetic device 5 andcorresponding to the period from the P wave to the QRS complex, anddisplays the same. Consequently, such an anatomical image as used in thefirst embodiment can be dispensed with to three-dimensionally identify apositional relationship of a part in myocardium providing un-uniformconduction of excitation.

[0106]FIG. 9 is a block diagram more specifically showing aconfiguration of the magnetocardiographic diagnosis apparatus of thesecond embodiment shown in FIG. 8.

[0107] With reference to FIG. 9, magnetic field distribution measurementdevice 1 will not be described as it is identical to that described withreference to FIGS. 2 and 3.

[0108] Magnetic field distribution measurement device 1 outputstime-series, magnetic field distribution data and outputs the data toarithmetic device 5 shown in FIG. 9. Arithmetic device 5 employs theanalysis technique using a current dipole, as described above, togenerate from time-series, magnetic field distribution data the dataregarding an intramyocardial excitation current.

[0109] Subject 12 has his/her electrocardiogram recorded by anelectrocardiograph 21 to allow measured electrocardiographic waveformdata of subject 12 to be fed to arithmetic device 5.

[0110] Note herein that if the electrocardiographically representedwaveform and the generated data regarding an intramyocardial excitationcurrent, the electrocardiogram and an event occurring in the heart canalso be correlated.

[0111] Reference will now be made to FIG. 10A schematically representinga normal stimulation conduction path in a heart and FIG. 10Brepresenting an electrocardiographically represented waveform for asingle heart beat.

[0112] With reference to FIGS. 10A and 10B, a sinoatrial node functionsas a pacemaker determining a heart beat and it fires at predeterminedintervals (a timing of a P wave of an electrocardiogram) to generate apulse. This pulse is transmitted through a specific stimulationconduction path to an atrioventricular node and therein after a periodof time elapses a pulse is transmitted through a bundle of His and aPurkinje fiber network to an underlying a ventricle and myocardialcontraction erupts. This conduction of a stimulation from the bundle ofHis to the Purkinje fiber network corresponds to the period of the QRScomplex in the electrocardiogram.

[0113] As such, by analyzing magnetocardiography related to the periodfrom the P wave to the QRS complex, i.e., by analyzing anintramyocardial excitation current, arithmetic device 5 generates imagedata representing a stimulation conduction path serving as a normalroute, as shown in FIG. 10A.

[0114] An image of a stimulation conduction path, such as shown in FIG.10A, can be used in place of the anatomical image used in the firstembodiment, as a template displayed. More specifically, athree-dimensional, anatomical image such as described in the firstembodiment can be dispensed with if a stimulation conduction path of anormal route, as shown in FIG. 10A, is displayed, since a part inmyocardium that exists in a neighboring ventricle and has a ventricularlate potential, i.e., provides un-uniform conduction of excitation wouldbe readily, anatomically correlated by a doctor and its location, sizeand geometry would be identified by the doctor.

[0115] Arithmetic device 5 shown in FIG. 9 generates data representing agenerated intramyocardial excitation conduction rate, superimposed on adisplaying of a stimulation conduction circuit as a template, such asdescribed above. As has been described previously, by noting an imagerepresenting an intramyocardial excitation conduction rate, in aventricle a part in myocardium providing un-uniform conduction ofexcitation or a part having a ventricular late potential can be found,and such image data can be combined with the aforementioned templateimage data and fed to display device 6.

[0116] Display device 6 shown in FIG. 9 uses the data received fromarithmetic device 5 to display an image representing an intramyocardialexcitation conduction rate, as superimposed on a normal stimulationconduction circuit serving as a template. Thus doctors can readilydetermine whether there is a condition allowing a reentry circuit to bereadily formed in ventricular muscle.

[0117]FIG. 11 exemplarily shows a screen actually displayed by displaydevice 6. It displays an image representing an intramyocardialexcitation conduction rate for each excitation conduction path,superimposed on a normal stimulation conduction circuit serving as atemplate.

[0118] In FIG. 11, two arrows are shown, each indicating the position ofan excitation conduction path approximated by a small current elementpiece (a current dipole). Each arrow has a length representing anexcitation conduction rate.

[0119] A doctor would be able to refer to a positional relationship of arespective excitation conduction path relative to the normal stimulationconduction path serving as a template, as shown in FIG. 11, to providean anatomical correlation and would also be able to refer to adifference in excitation conduction rate between excitation conductionpaths to identify the location, size and geometry of a part in aventricle that has a ventricular late potential, i.e., a part inmyocardium that provides un-uniform conduction of excitation.

[0120]FIGS. 12 and 13 are a flow chart representing a method effected bythe magnetocardiographic diagnosis apparatus of the second embodiment toidentify a part in myocardium providing un-uniform conduction ofexcitation.

[0121] Initially, with reference to FIG. 12, at step S11 magnetic fielddistribution measurement device 1 is used to provide a non-contactmagnetic measurement on the chest of a human body at a plurality ofcoordinates to generate and record a plurality of time-series magneticdata.

[0122] Then at step S12 an analysis start time point is set tocorrespond to an electrocardiographically represented P-wave start timepoint t_(sP), an analysis end time point to an electrocardiographicallyrepresented QRS-complex end time point t_(eQRS), and an analysis timeinterval to Δt.

[0123] Then at step S13 time point t_(SP) is substituted into analysistime point t.

[0124] Then at step S14 until an analysis time reaches time pointt_(eQRS) the following steps S15-S17 are repeated.

[0125] More specifically at step S15 arithmetic device 5 approximatesmagnetocardiographic distribution data of a designated analysis timepoint t with one or more small current element pieces to obtain dataregarding the location, direction and magnitude of an intramyocardialexcitation current.

[0126] Then at step S16 the data of the intramyocardial excitationcurrent obtained at step S16 undergoes three-dimensional, perspectiveconversion from a predetermined point of view and displayed in an image.

[0127] Then at step S17 Δt is added to analysis time point t and theprocess returns to step S14 and a decision is made as to whether timepoint t_(eQRS) has been reached. If so then it means that there has beenobtained image data representing a stimulation conduction pathcorresponding to a normal route, as shown in FIG. 10A, as correspondingin an electrocardiographically represented waveform to the period fromthe P wave to the QRS complex.

[0128] Then the process proceeds with step S18, shown in FIG. 13, and ananalysis start time point, an analysis end time point and an analysistime interval are set to be t_(s), t_(e) and Δt, respectively.

[0129] Then at step S19 analysis start time point t_(s) is substitutedinto analysis time point t.

[0130] Then at step S20 until a decision is made that analysis timepoint t has reached analysis end time point t_(e) the following stepsS21-S24 are effected in a loop.

[0131] More specifically, at step S21 arithmetic device 5 approximatemagnetocardiographic distribution data of designated analysis time twith one or more small current element pieces to obtain data regardingthe location, direction and magnitude of an intramyocardial excitationcurrent.

[0132] Then at step S22 the data of the location, direction andmagnitude of the intramyocardial excitation current at time point t-Δt,as obtained at step S21 of the previous loop preceding by time Δt, iscompared to the data corresponding to time point t, as obtained at stepS21 of the current loop, and an intramyocardial excitation conductionrate is calculated.

[0133] Then at step S23 display device 4 displays data representing anintramyocardial excitation conduction rate, as superimposed on an imageof a normal stimulation conduction path having undergone athree-dimensional, perspective conversion from a predetermined point ofview.

[0134] Furthermore at step S24 Δt is added to analysis time point t andthe process returns to step S20 and a decision is made as to whetheranalysis end time t_(e) has been reached. Thus data representing anintramyocardial excitation conduction rate is superimposed on anddisplayed together with an image of a stimulation conduction path (FIG.10A) obtained through the FIG. 12 flow chart.

[0135] Thus in the second embodiment an image representing anintramyocardial excitation conduction rate obtained from a SQUIDmagnetometer obtaining a non-invasive magnetic measurement on asubject's chest can be superimposed on a normal stimulation conductionpath serving as a template and it can thus be displayed to eliminate thenecessity of superimposing it on an anatomical image to allow a doctorto three-dimensionally identify the positional relationship, size andgeometry of a-part in myocardium having a ventricular late potential,i.e., a part in myocardium providing un-uniform conduction of excitationthat might cause ventricular tachycardia, as seen relative to astimulation conduction path. As such the second embodiment can eliminatethe necessity of previously conducting a test to obtain the anatomicalimage.

[0136] In particular, if high frequency catheter cauterization is usedto provide a treatment, it can previously, significantly narrow down aregion to be electrophysiologically tested using a catheter and a testconducted while radioscopy is provided can be conducted in asignificantly reduced period of time. Consequently, doctors andradiographers can avoid significantly large annual doses of x-rayexposure.

[0137] Furthermore, using the method of identifying a part in myocardiumproviding un-uniform conduction of excitation, as described in thesecond embodiment, together with high frequency catheter cauterizationallows a less invasive medical operation to be used to treat ventriculartachycardia and thus further alleviate a burden on patients.

[0138] Note that in the second embodiment, in creating image data of anormal stimulation conduction path displayed as a template a currentdipole is used to approximate an excitation conduction path. Such animage of a normal stimulation conduction path can be obtained byoperating operation unit 5 to obtain an intramyocardial current densitydistribution from time-series, magnetic field distribution datagenerated by magnetic field distribution measurement device 1, and theintramyocardial current distribution density can be obtained from thetime-series, magnetic field distribution data by employing syntheticaperture magnetometric (SMA), multiple signal classification (MUSIC) orother similar, various techniques. SAM and MUSIC have been studied anddeveloped for example in the fields of radar and sonar and are wellknown techniques. However, they have hitherto been unapplied tomagnetocardiographic diagnosis.

[0139] SAM and MUSIC are well known techniques and the algorithms usingthese techniques to obtain a current density distribution aresignificantly complicated, and they will not be described specifically.SAM is specifically described by Robinson S E and Vrba J, “FunctionalNeuroimaging by Synthetic Aperture Magnetometry (SAM)” in Proceedings ofthe 11th International Conference on Biomagnetism, “Reent Advances inBiomagnetism,” published by Tohoku University Press, 1999, pp. 302-305.MUSIC is specifically described by Hiroshi Hara and Shinya Kurishiro,“Science of Cerebric Magnetism-SQUID Measurement and MedicalApplications,” published by Ohmsha, Jan. 25, 1997, pp. 117-119.

[0140] Thus in accordance with the-present invention an intramyocardialexcitation conduction rate obtained through a non-invasive magneticmeasurement on a patient's chest can be displayed visibly on athree-dimensional, anatomical image to allow three-dimensionalidentification of the location, size and geometry of a part having aventricular late potential, i.e., a part in myocardium providingun-uniform conduction of excitation. This allows a non-invasivediagnosis of a part in myocardium providing un-uniform conduction ofexcitation or having a ventricular late potential that might causeventricular tachycardia. As such, without imposing a burden on patientsa rapid and safe test can be-conducted.

[0141] In particular, if high frequency catheter ablation is used toprovide a treatment, it can previously, significantly narrow down aregion to be electrophysiologically tested and thus effectively,significantly reduce doses of x ray radiation that are received bydoctors and radiographers.

[0142] In accordance with the present invention in still another aspecta subject's intramyocardial excitation conduction rate can besuperimposed on the same subject's normal stimulation conduction pathfrom a sinoatrial node to a bundle of His-Purkinje fiber network toeliminate the necessity of obtaining an anatomical image tothree-dimensionally identify the position of a part in myocardiumproviding un-uniform conduction of excitation, i.e., the localizationand spread of a ventricular late potential. Furthermore, a testconducted to obtain the anatomical image can be eliminated and moreeconomically efficient diagnosis can thus be provided.

Industrial Applicability

[0143] Thus in accordance with the present invention amagnetocardiographic diagnosis apparatus for a ventricular latepotential and a method of identifying a part in myocardium providingun-uniform conduction of excitation can three-dimensionally identify theposition, size and geometry of the part in myocardium providingun-uniform conduction of excitation. It is useful in non-invasivelydiagnosing a part in myocardium providing un-uniform conduction ofexcitation or having a ventricular late potential that might causeventricular tachycardia.

1. A magnetocardiographic diagnosis apparatus for ventricular latepotential, comprising: a magnetic field distribution measurement device(1) performing a non-contact magnetic measurement on a subject's chestat a plurality of coordinates to obtain a plurality of time-seriesmagnetic data corresponding to said plurality of coordinates, and alsousing said plurality of time-series magnetic data to generatetime-series magnetic field distribution data on said chest; a firstarithmetic device (2) using said generated time-series magnetic fielddistribution data to generate data representative of athree-dimensional, intramyocardial, electrical behavior of said subject;a second arithmetic device (3) processing separately provided,tomographic, thoracic data of said subject to generate datarepresentative of an anatomical image; and a display device (4)displaying an image of said three-dimensional, intramyocardial,electrical behavior represented by said data generated by said firstarithmetic device, as superimposed on said anatomical image representedby said data generated by said second arithmetic device, thereby capableof three-dimensionally identifying localization of a ventricular latepotential attributed to intramyocardial, un-uniform conduction ofexcitation.
 2. The apparatus of claim 1, wherein said data generated bysaid first arithmetic device and representative of saidthree-dimensional, intramyocardial, electrical behavior is datarepresentative of an intramyocardial excitation conduction rate.
 3. Theapparatus of claim 2, wherein said first arithmetic device approximatesby means of one or more small current element pieces a part inmyocardium corresponding to an excitation conduction path and calculatesa temporal variation of a position of said small current element pieceto generate data representative of an intramyocardial excitationconduction rate.
 4. The apparatus of claim 3, wherein said firstarithmetic device operates based on said calculated temporal variationof the position of said small current element piece to generate datarepresentative of a difference in intramyocardial excitation conductionrate for each excitation conduction path.
 5. A magnetocardiographicdiagnosis apparatus for ventricular late potential, comprising: amagnetic field distribution measurement device (1) performing anon-contact magnetic measurement on a subject's chest at a plurality ofcoordinates to obtain a plurality of time-series magnetic datacorresponding to said plurality of coordinates, and also using saidplurality of time-series magnetic data to generate time-series magneticfield distribution data on said chest; an arithmetic device (5) usingsaid generated time-series magnetic field distribution data to generatedata representative of a three-dimensional, intramyocardial, electricalbehavior of said subject; and a display device (6) using the datagenerated by said arithmetic device to superimpose together an imagerepresenting a stimulation conduction path of said subject extendingfrom a sinoatrial node to a bundle of His-Purkinje fiber network and animage representing a three-dimensional, intramyocardial, electricalbehavior and display said images, thereby capable of three-dimensionallyidentifying localization of a ventricular late potential attributed tointramyocardial, un-uniform conduction of excitation.
 6. The apparatusof claim 5, wherein the data generated by said arithmetic device andrepresentative of said three-dimensional, intramyocardial, electricalbehavior is data representative of an intramyocardial excitationconduction rate.
 7. The apparatus of claim 6, wherein said arithmeticdevice approximates by means of one or more small current element piecesa part in myocardium corresponding to an excitation conduction path andcalculates a temporal variation of a position of said small currentelement piece to generate data representative of said intramyocardialexcitation conduction rate.
 8. The apparatus of claim 7, wherein saidarithmetic device operates based on said calculated temporal variationof the position of said small current element piece to generate datarepresentative of a difference in intramyocardial excitation conductionrate for each excitation conduction path.
 9. A method of identifying apart in myocardium providing un-uniform conduction of excitation,comprising the steps of: performing a non-contact magnetic measurementon a subject's chest at a plurality of coordinates to obtain a pluralityof time-series magnetic data corresponding to said plurality ofcoordinates and used to generate time-series magnetic field distributiondata of said chest and generating first data representative of athree-dimensional, intramyocardial, electrical behavior of said subjectfrom the generated time-series magnetic field distribution data;processing separately fed, tomographic, thoracic image data of saidsubject to generate second data representative of an anatomical image;and displaying an image of said three-dimensional, intramyocardial,electrical behavior represented by said first data, as superimposed onsaid anatomical image represented by said second data, to allowthree-dimensional identification of localization of a ventricular latepotential attributed to intramyocardial, un-uniform conduction ofexcitation.
 10. The method of claim 9, wherein said three-dimensional,intramyocardial, electrical behavior represented by said first data isan intramyocardial excitation conduction rate.
 11. The method of claim10, wherein the step of generating said first data uses one or moresmall current element pieces to approximate a part in myocardiumcorresponding to an excitation conduction path and calculates a temporalvariation of a position of said small current element piece to generatedata representative of said intramyocardial excitation conduction rate.12. The method of claim 11, wherein the step of generating said firstdata uses said calculated temporal variation of the position of saidsmall current element piece to generate data representative of adifference in excitation conduction rate for each excitation conductionpath.
 13. A method of identifying a part in myocardium providingun-uniform conduction of excitation, comprising the steps of: performinga non-contact magnetic measurement on a subject's chest at a pluralityof coordinates to obtain a plurality of time-series magnetic datacorresponding to said plurality of coordinates and used to generatetime-series magnetic field distribution data of said chest andgenerating data representative of a three-dimensional, intramyocardial,electrical behavior of said subject from the generated time-seriesmagnetic field distribution data; and using said generated data tosuperimpose together an image representing a stimulation conduction pathof said subject extending from a sinoatrial node to a bundle ofHis-Purkinje fiber network and an image representing athree-dimensional, intramyocardial, electrical behavior, and thusdisplaying said images to allow three-dimensional identification oflocalization of a ventricular late potential attributed tointramyocardial, un-uniform conduction of excitation.
 14. The method ofclaim 13, wherein said three-dimensional, intramyocardial, electricalbehavior represented by said data is an intramyocardial excitationconduction rate.
 15. The method of claim 14, wherein the step ofgenerating said data uses one or more small current element pieces toapproximate a part in myocardium corresponding to an excitationconduction path and calculates a temporal variation of a position ofsaid small current element piece to generate data representative of saidintramyocardial excitation conduction rate.
 16. The method of claim 15,wherein the step of generating said data uses said calculated temporalvariation of the position of said small current element piece togenerate data representative of a difference in said intramyocardialexcitation conduction rate of each excitation conduction path.